The major goals of this project are to identify mechanisms of protective immunity against parasitic infections while at the same time studying mechanisms by which parasites evade the immune response. In schistosomiasis, these studies involve the identification of effector mechanisms by which schistosomula are killed in mice with either concomitant or irradiated cercarial vaccine-induced immunity to challenge infection. In particular, the role of activated macrophages in schistosomulum killing has been closely analyzed. Schistosomes were also studied in terms of their ability to evade host immune responses and the possibility that they actively mimic the host, analyzed by assaying the genome of the parasite for hybridization with host total DNA as well as cDNA probes. In another study, an approach to immunization against parasites employing anti-idiotype antibodies was explored, and in preliminary experiments the injection of these antibodies was found to partially protect mice against a variant of African trypanosomiasis. The role of the alternative complement pathway (ACP) as a defense against parasitic infection was studied with the protozoa Trichomonas vaginalis and Trypanosoma cruzi, and a millipore chamber implantation technique was developed for inducing the transformation of ACP sensitive epimastigotes into ACP resistant trypomastigotes in mice.